Next permutation

Signed-off-by: begeekmyfriend <[email protected]>

031_next_permutation/Makefile

@@ -0,0 +1,2 @@
+all:
+	gcc -O2 -o test next_permutation.c

031_next_permutation/next_permutation.c

@@ -0,0 +1,63 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+static void reverse(int *a, int size)
+{
+    int left = 0;
+    int right = size - 1;
+    while (left < right) {
+        int tmp = a[left];
+        a[left] = a[right];
+        a[right] = tmp;
+        left++;
+        right--;
+    }
+}
+
+void nextPermutation(int* nums, int numsSize) {
+    if (numsSize <= 1) {
+        return;
+    }
+
+    int *p = nums + numsSize - 1;    
+    int *q = nums + numsSize - 1;
+
+    while (p != nums && *(p - 1) >= *p) {
+        p--;
+    }
+
+    if (p != nums) {
+        int n = *(p - 1);
+        while (*q <= n) {
+            q--;
+        }
+
+        int tmp = *q;
+        *q = *(p - 1);
+        *(p - 1) = tmp;
+    }
+    reverse(p, numsSize - (p - nums));
+}
+
+int main(int argc, char **argv)
+{
+    if (argc <= 1) {
+        fprintf(stderr, "Usage: ./test ...\n");
+        exit(-1);
+    }
+
+    int i;
+    int *nums = malloc(sizeof(int));
+    for (i = 0; i < argc - 1; i++) {
+        nums[i] = atoi(argv[i + 1]);
+    }
+
+    nextPermutation(nums, argc - 1);
+
+    for (i = 0; i < argc - 1; i++) {
+        printf("%d", nums[i]);
+    }
+    putchar('\n');
+
+    return 0;
+}